The present invention relates to a method and an apparatus for inspecting patterns which are capable of inspecting a high density pattern having repeated pattern portions, such as a reticle or a mask used for very large scale integration (VLSI) memories, etc., at a high speed.
Patterns for recent VLSIs, particularly patterns for 256K-bit or 1M-bit memories, are almost entirely oriented to high integration density and large capacity. For example, from the point of view of the level of original data used for a pattern generator, as many as 10.sup.7 pattern portions or pattern elements are included on a single chip, with an integration density of 5000 patterns portions/mm.sup.2, or more. The inspection of either a high density pattern of a reticle, formed by a pattern generator on the basis of original data, or the high density of pattern portions on a mask substrate, is often carried by comparing and collating a signal obtained by scanning a mask substrate and a signal of the same level obtained from the original data stored on a magnetic tape. The large volume of original data required for a VLSI, however, creates problems in storing and converting the data.
In the case of a VLSI, it is difficult to convert the original data stored on a magnetic tape to original pattern data in accordance with the scanning of a mask substrate in order to perform an inspection, since an increase of the pattern density makes the original data more complicated and a longer time is required to convert original data corresponding to a constant scanning range to original pattern data than to scan the mask substrate. As a result, the scanning speed of mask substrate must be lowered and the inspection time is increased.